The invention relates to a fuel injection apparatus having a work chamber enclosed within a cylinder by a pump piston, the work chamber being connectable with a fuel injection location by at least one supply line, and also being connectable during the piston intake stroke, with a fuel inlet conduit leading to a fuel supply source and having a fuel quantity device which is electrically actuatable by a control unit.
In an injection apparatus of this kind, known from German Offenlegungsschrift No. 19 19 969, the fuel quantity which is to be injected during the supply stroke of the pump piston of an injection pump is metered during the intake stroke of the pump piston by a magnetic valve which is controlled in either a cyclic or an analog manner. The metered quantity is determined by the open period of the magnetic valve, and the open phase of this valve is disposed exclusively within the period of the intake stroke of the pump piston. In this known apparatus, pressure conditions in the work chamber and the valve cross section of the fuel injection pump determine the metered quantity. For precise metering of the fuel injection quantity in this known apparatus, the rpm and the injection instant must be taken into consideration in dimensioning the opening periods of the magnetic valve. The pressure fluctuations in the work chamber during the filling process must also be considered. Further disadvantages are associated with the limited switching speed of the magnetic valve. The two switching processes of the magnetic valve occurring during the intake stroke thus influence the precision of the metered result. The rpm or the injection rpm are also limited by the switching time of the magnetic valve.
In another fuel injection pump, known from German Offenlegungsschrift No. 19 19 707, the limited switching speed of magnetic valves is taken into consideration in that two pumping systems are accommodated in the distributor of this distributor-type pump, each pumping system being supplied with fuel by one magnetic valve. In this manner, a higher pump rpm can be obtained. The cam drive of the pump pistons in this injection pump is also embodied such that the stroke speed of the pump piston during the intake stroke is substantially slower than that during the supply stroke of the pump piston. The magnetic valve of each pumping system of this radial-piston pump is likewise opened exclusively during the intake stroke of the pump piston, and the duration of opening of the magnetic valve determines the metered quantity. Here again, the rpm and the adjustment of injection timing must be taken into consideration in controlling magnetic valves. In designing this pump, the metering cycle of the magnetic valve begins with the intake stroke of the associated pump pistons. An adjustment of injection onset dictates a change in the onset of the intake stroke, so that this intake stroke onset must be furnished precisely in calculating the opening period of the magnetic valve. Dynamic conditions at the switchover point of the pump piston, that is, at the transition from the supply stroke to the intake stroke are also difficult to control. Because of the double pumping system in this fuel injection pump, the apparatus is also very expensive.